:root {
    --primary-blue: #2196F3;
    --success-green: #4CAF50;
    --warning-yellow: #FFC107;
    --danger-red: #F44336;
    --accent-purple: #9C27B0;
    --background: #f5f5f5;
    --surface: #ffffff;
    --text-primary: #333333;
    --text-secondary: #666666;
    --border: #e0e0e0;
    --shadow: 0 2px 8px rgba(0,0,0,0.1);
    --border-radius: 12px;
    --transition: all 0.3s ease;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: var(--background);
    color: var(--text-primary);
    line-height: 1.6;
    padding-bottom: 80px;
}

.app-header {
    background: linear-gradient(135deg, var(--primary-blue), var(--accent-purple));
    color: white;
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.app-header h1 {
    font-size: 1.5rem;
    font-weight: 600;
}

.user-info {
    font-size: 0.9rem;
    background: rgba(255,255,255,0.2);
    padding: 0.5rem 1rem;
    border-radius: 20px;
}

.app-main {
    padding: 1rem;
    max-width: 600px;
    margin: 0 auto;
}

.section {
    display: none;
    animation: fadeIn 0.3s ease;
}

.section.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Mood Selector */
.mood-selector {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

.mood-selector h2 {
    text-align: center;
    margin-bottom: 1.5rem;
    color: var(--primary-blue);
}

.mood-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 1rem;
}

.mood-btn {
    background: var(--surface);
    border: 2px solid var(--border);
    border-radius: var(--border-radius);
    padding: 1rem;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
}

.mood-btn:hover {
    border-color: var(--primary-blue);
    transform: translateY(-2px);
}

.mood-btn.active {
    border-color: var(--primary-blue);
    background: rgba(33, 150, 243, 0.1);
}

.mood-emoji {
    font-size: 2rem;
}

.mood-label {
    font-size: 0.9rem;
    font-weight: 500;
}

/* Activity Selector */
.activity-selector {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

.activity-selector h3 {
    text-align: center;
    margin-bottom: 1.5rem;
    color: var(--success-green);
}

.activity-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
    gap: 1rem;
}

.activity-btn {
    background: var(--surface);
    border: 2px solid var(--border);
    border-radius: var(--border-radius);
    padding: 1rem;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
}

.activity-btn:hover {
    border-color: var(--success-green);
    transform: translateY(-2px);
}

.activity-btn.active {
    border-color: var(--success-green);
    background: rgba(76, 175, 80, 0.1);
}

.activity-btn i {
    font-size: 1.5rem;
    color: var(--success-green);
}

.activity-btn span {
    font-size: 0.8rem;
    font-weight: 500;
}

/* Current Selection */
.current-selection {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    text-align: center;
}

.selection-display {
    margin-bottom: 1rem;
}

.selection-display p {
    margin-bottom: 0.5rem;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-blue), var(--accent-purple));
    color: white;
    border: none;
    padding: 1rem 2rem;
    border-radius: var(--border-radius);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(33, 150, 243, 0.3);
}

.btn-primary:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Player */
.player-container {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

.current-track {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border);
}

.track-info h3 {
    color: var(--primary-blue);
    margin-bottom: 0.5rem;
}

.track-info p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.track-mood {
    font-size: 1.5rem;
}

.player-controls {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1.5rem;
}

.control-btn {
    background: var(--surface);
    border: 2px solid var(--primary-blue);
    border-radius: 50%;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: var(--transition);
    color: var(--primary-blue);
}

.control-btn:hover {
    background: var(--primary-blue);
    color: white;
}

.play-btn {
    width: 60px;
    height: 60px;
    font-size: 1.2rem;
}

.progress-container {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.progress-bar {
    flex: 1;
    height: 6px;
    background: var(--border);
    border-radius: 3px;
    overflow: hidden;
}

.progress {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-blue), var(--accent-purple));
    width: 0%;
    transition: width 0.1s ease;
}

.volume-container {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.volume-container i {
    color: var(--text-secondary);
}

#volume-slider {
    flex: 1;
    height: 6px;
    background: var(--border);
    border-radius: 3px;
    outline: none;
    -webkit-appearance: none;
}

#volume-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 16px;
    height: 16px;
    background: var(--primary-blue);
    border-radius: 50%;
    cursor: pointer;
}

/* Playlist */
.playlist-container {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
}

.playlist-container h3 {
    margin-bottom: 1rem;
    color: var(--success-green);
}

.playlist {
    max-height: 300px;
    overflow-y: auto;
}

.playlist-item {
    display: flex;
    align-items: center;
    padding: 0.75rem;
    border-radius: 8px;
    margin-bottom: 0.5rem;
    cursor: pointer;
    transition: var(--transition);
    border: 1px solid transparent;
}

.playlist-item:hover {
    background: var(--background);
    border-color: var(--primary-blue);
}

.playlist-item.active {
    background: rgba(33, 150, 243, 0.1);
    border-color: var(--primary-blue);
}

.playlist-item .track-number {
    width: 30px;
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.playlist-item .track-details {
    flex: 1;
    margin-left: 1rem;
}

.playlist-item .track-title {
    font-weight: 500;
    margin-bottom: 0.25rem;
}

.playlist-item .track-artist {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.playlist-item .track-mood {
    font-size: 1.2rem;
}

.empty-playlist {
    text-align: center;
    color: var(--text-secondary);
    padding: 2rem;
}

/* History */
.history-container {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
}

.mood-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
}

.stat-card {
    background: var(--background);
    padding: 1rem;
    border-radius: var(--border-radius);
    text-align: center;
}

.stat-card h4 {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 0.5rem;
}

.stat-value {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--primary-blue);
}

.mood-history h3 {
    margin-bottom: 1rem;
    color: var(--accent-purple);
}

.history-list {
    max-height: 300px;
    overflow-y: auto;
}

.history-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    background: var(--background);
    border-radius: 8px;
    margin-bottom: 0.5rem;
}

.history-item .mood-activity {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.history-item .timestamp {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.empty-history {
    text-align: center;
    color: var(--text-secondary);
    padding: 2rem;
}

.learning-insights {
    margin-top: 2rem;
}

.learning-insights h3 {
    margin-bottom: 1rem;
    color: var(--warning-yellow);
}

.insights-list {
    background: var(--background);
    padding: 1rem;
    border-radius: var(--border-radius);
}

.insight-item {
    padding: 0.5rem 0;
    border-bottom: 1px solid var(--border);
}

.insight-item:last-child {
    border-bottom: none;
}

/* Settings */
.settings-container {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
}

.setting-group {
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border);
}

.setting-group:last-child {
    border-bottom: none;
}

.setting-group h3 {
    margin-bottom: 1rem;
    color: var(--primary-blue);
}

.setting-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.75rem 0;
}

.setting-item label {
    font-weight: 500;
}

.setting-item input[type="checkbox"] {
    width: 20px;
    height: 20px;
    accent-color: var(--primary-blue);
}

.setting-item input[type="range"] {
    width: 100px;
    margin-right: 1rem;
}

.btn-secondary {
    background: var(--text-secondary);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    margin-right: 1rem;
    margin-bottom: 0.5rem;
}

.btn-secondary:hover {
    background: var(--text-primary);
}

.btn-danger {
    background: var(--danger-red);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
}

.btn-danger:hover {
    background: #d32f2f;
}

/* FAQ */
.faq-section {
    background: var(--surface);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin: 1.5rem 1rem;
    box-shadow: var(--shadow);
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.faq-section h2 {
    text-align: center;
    margin-bottom: 1.5rem;
    color: var(--primary-blue);
}

.faq-item {
    border-bottom: 1px solid var(--border);
    margin-bottom: 1rem;
}

.faq-item:last-child {
    border-bottom: none;
}

.faq-question {
    width: 100%;
    background: none;
    border: none;
    padding: 1rem 0;
    text-align: left;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: var(--text-primary);
    transition: var(--transition);
}

.faq-question:hover {
    color: var(--primary-blue);
}

.faq-icon {
    font-size: 1.2rem;
    color: var(--primary-blue);
    transition: var(--transition);
}

.faq-question[aria-expanded="true"] .faq-icon {
    transform: rotate(45deg);
}

.faq-answer {
    padding: 0 0 1rem 0;
    color: var(--text-secondary);
    line-height: 1.6;
    animation: slideDown 0.3s ease;
}

.faq-answer[hidden] {
    display: none;
}

@keyframes slideDown {
    from {
        opacity: 0;
        max-height: 0;
    }
    to {
        opacity: 1;
        max-height: 200px;
    }
}

/* Bottom Navigation */
.bottom-nav {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: var(--surface);
    border-top: 1px solid var(--border);
    display: flex;
    justify-content: around;
    padding: 0.5rem 0;
    z-index: 100;
}

.nav-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    text-decoration: none;
    color: var(--text-secondary);
    transition: var(--transition);
    padding: 0.5rem;
    border-radius: 8px;
    min-width: 60px;
}

.nav-item:hover,
.nav-item.active {
    color: var(--primary-blue);
    background: rgba(33, 150, 243, 0.1);
}

.nav-item i {
    font-size: 1.2rem;
    margin-bottom: 0.25rem;
}

.nav-item span {
    font-size: 0.7rem;
    font-weight: 500;
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem 1rem;
    color: var(--text-secondary);
    font-size: 0.8rem;
    background: var(--surface);
    margin-top: 2rem;
}

/* Responsive Design */
@media (max-width: 480px) {
    .app-header {
        padding: 0.75rem;
    }
    
    .app-header h1 {
        font-size: 1.2rem;
    }
    
    .mood-grid,
    .activity-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .mood-stats {
        grid-template-columns: 1fr;
    }
    
    .current-track {
        flex-direction: column;
        align-items: flex-start;
        gap: 1rem;
    }
    
    .player-controls {
        gap: 0.5rem;
    }
    
    .control-btn {
        width: 45px;
        height: 45px;
    }
    
    .play-btn {
        width: 55px;
        height: 55px;
    }
}

@media (min-width: 768px) {
    .app-main {
        padding: 2rem;
    }
    
    .mood-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .activity-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .bottom-nav {
        position: relative;
        border: 1px solid var(--border);
        border-radius: var(--border-radius);
        margin: 2rem auto;
        max-width: 600px;
    }
    
    body {
        padding-bottom: 0;
    }
}

/* Loading Animation */
.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 2px solid var(--border);
    border-radius: 50%;
    border-top-color: var(--primary-blue);
    animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Notification */
.notification {
    position: fixed;
    top: 80px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--primary-blue);
    color: white;
    padding: 1rem 1.5rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    z-index: 1000;
    animation: slideInDown 0.3s ease;
}

.notification.success {
    background: var(--success-green);
}

.notification.error {
    background: var(--danger-red);
}

@keyframes slideInDown {
    from {
        opacity: 0;
        transform: translate(-50%, -20px);
    }
    to {
        opacity: 1;
        transform: translate(-50%, 0);
    }
}